The present invention relates to the fabrication of integrated circuits. In particular, the invention provides a technique, including a method and apparatus, for control of the deposition of a dielectric film having a reduced dielectric constant. In addition, the dielectric film can also be made to resist outgassing and shrinkage by the novel use of low-frequency radio-frequency (RF) power.
Many very large scale integrated (VLSI) semiconductor devices employ multilevel interconnects to increase the packing density of devices on a substrate. Typically, such devices include intermetal dielectric (IMD) layers that insulate adjacent metalization layers from one another. The capacitance between these metalization layers may be reduced by reducing the dielectric constant of the IMD between them. The dielectric constant of these layers has a direct impact on the size of device that can be produced. For example, one semiconductor industry association projects that the ability to mass produce sub-0.25 .mu.m devices will require the use of IMD layers having dielectric constants of 2.9 or less. Thus, there is a continuing need for IMD layers having reduced dielectric constants.
Other properties of these IMD layers are also important. For example, IMD layers should have good "gap-fill" characteristics, namely, the layers should exhibit good step coverage and planarization properties to produce void-free layers that not only completely fill steps and openings in the underlying substrate, but also form smooth planarized dielectric layers. The layers should be able to be deposited at low temperatures, preferably below about 400.degree. C. to avoid damage to underlying metalization layers.
A number of existing approaches to the deposition of IMD layers include the formation and deposition of several layers of silicon oxide film. This deposition typically is performed using chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired film. Other processes use a plasma to deposit the film (plasma-enhanced CVD, or PECVD). Other deposition techniques employ halogen dopants to reduce the deposited film's dielectric constant and improve gap-filling capabilities. Although these films have been found to possess desirable qualities and are well-suited for some applications, other applications may require the use of films having even lower dielectric constants. There is, accordingly, a need for dielectric films having reduced dielectric constants that are suitable for use in these other applications.
Moreover, such low-dielectric films should exhibit good film stability. This is especially true with respect to the stability of halogen-doped films, which may experience unacceptable levels of outgassing and shrinkage, for example. Also of concern in commercial environments is the substrate processing system's throughput. System throughput may be increased by maximizing the rate at which the substrate processing system deposits a film. Thus, it is desirable to maximize the film's deposition rate.
What is therefore needed is a process by which a film, having a reduced dielectric constant and good gap-filling capabilities, may be deposited at an acceptable rate. Moreover, a film so deposited should exhibit acceptable stability.